Dehydrocyclization with an acidic multimetallic catalytic composite

ABSTRACT

Dehydrocyclizable hydrocarbons are converted to aromatics by contacting them at dehydrocyclization conditions with an acidic multi-metallic catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a rhenium component, a cobalt component, and a halogen component with a porous carrier material. The platinum group component, rhenium component, cobalt component, and halogen component are present in the multimetallic catalyst in amounts respectively, calculated on an elemental basis, corresponding to about 0.01 to about 2 wt. % platinum group metal, about 0.1 to about 5 wt. % cobalt, about 0.01 to about 2 wt. % rhenium, and about 0.1 to about 3.5 wt. % halogen. Moreover, the catalytically active sites induced by these metallic components are uniformly dispersed throughout the porous carrier material and these metallic components are present in the catalyst in carefully controlled oxidation states such that substantially all of the platinum group component is present therein in the elemental metallic state and substantially all of the rhenium and catalytically available cobalt components are present in the elemental metallic state or in a state which is reducible to the elemental metallic state under dehydrocyclization conditions, or in a mixture of these states. A specific example of dehydrocyclization method disclosed herein is a method for converting a feed mixture of n-hexane and n-heptane to a product mixture of benzene and toluene which involves contacting the feed mixture and a hydrogen stream with the acidic multimetallic catalyst disclosed herein at dehydrocyclization conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my prior, copendingapplication Ser. No. 550,083 filed Feb. 4, 1975 (now U.S. Pat. No.3,939,059). All of the teachings of this prior application arespecifically incorporated herein by reference.

The subject of the present invention is, broadly, an improved method fordehydrocyclizing a dehydrocyclizable hydrocarbon to produce an aromatichydrocarbon. In a narrower aspect, the present invention involves amethod of dehydrocyclizing aliphatic hydrocarbons containing 6 to 20carbon atoms per molecule to monocyclic aromatic hydrocarbons withminimum production of side products such as C₁ to C₅ hydrocarbons,bicyclic aromatics, olefins and coke. In another aspect, the presentinvention relates to the dehydrocyclization use of an acidicmultimetallic catalytic composite comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a rhenium component, and a halogen component with a porouscarrier material. This acidic multimetallic composite has been found topossess highly beneficial characteristics of activity, selectively, andstability when it is employed in the dehydrocyclization ofdehydrocyclizable hydrocarbons to make aromatics such as benzene,toluene and xylene.

The conception of the present information followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking and isomerization function, andsuperior conversion, selectivity, and stability characteristics whenemployed in hydrocarbon conversion processes that have traditionallyutilized dual-function catalytic composites. In my prior applications, Idisclosed a significant finding with respect to a multimetalliccatalytic composite meeting these requirements. More specifically, Idetermined that a combination of specified amounts of a cobalt componentand a rhenium component can be utilized, under certain conditions, tobeneficially interact with the platinum group component of adual-function acidic catalyst with a resultant marked improvement in theperformance of such a catalyst. Now I have ascertained that an acidicmultimetallic catalytic composite, comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a rhenium component and a halogen component with a porouscarrier material can have superior activity, selectivity, and stabilitycharacteristics when it is employed in a ring-closure ordehydrocyclization process if the catalytically active sites induced bythese components are uniformly dispersed in the porous carrier materialin the amounts specified hereinafter and if the oxidation state of theactive metallic ingredients are carefully controlled so thatsubstantially all of the platinum group component is present in theelemental metallic state and substantially all of the rhenium andcatalytically available cobalt components are present in the elementalmetallic state or in a state which is reducible to the elementalmetallic state under dehydrocyclization conditions or in a mixture ofthese states.

The dehydrocyclization of dehydrocyclizable hydrocarbons is an importantcommercial process because of the great and expanding demand foraromatic hydrocarbons for use in the manufacture of various chemicalproducts such as synthetic fibers, insecticides, adhesives, detergents,plastics, synthetic rubbers, pharmaceutical products, high octanegasoline, perfumes, drying oils, ion-exchange resins, and various otherproducts well known to those skilled in the art. One example of thisdemand is in the manufacture of alkylated aromatics such asethylbenzene, cumene and dodecylbenzene by using the appropriatemono-olefins to alkylate benzene. Another example of this demand is inthe area of chlorination of benzene to give chlorobenzene which is thenused to prepare phenol by hydrolysis with soldium hydroxide. The chiefuse for phenol is of course in the manufacture of phenol-formaldehyderesins and plastics. Another route to phenol uses cumene as a startingmaterial and involves the oxidation of cumene by air to cumenehydroperoxide which can then be decomposed to phenol and acetone by theaction of an appropriate acid. The demand for ethylbenzene is primarilyderived from its use to manufacture styrene by selectivedehydrogenation; styrene is in turn used to make styrene-butadienerubber and polystyrene. Ortho-xylene is typically oxidized to phthalicanhydride by reaction in vapor phase with air in the presence of avanadium pentoxide catalyst. Phthalic anhydride is in turn used forproduction of plasticizers, polyesters and resins. The demand forpara-xylene is caused primarily by its use in the manufacture ofterephthalic acid or dimethyl terephthalate which in turn is reactedwith ethylne glycol and polymerized to yield polyester fibers.Substantial demand for benzene also is associated with its use toproduce aniline, Nylon, maleic anhydride, solvents and the likepetrochemical products. Toluene, on the other hand, is not at leastrelative to benzene and the C₈ aromatics, in great demand in thepetrochemical industry as a basic building block chemical; consequently,substantial quantities of toluene are hydrodealkylated to benzene ordisproportionated to benzene and xylene. Another use for toluene isassociated with the transalkylation of trimethylbenzene with toluene toyield xylene.

Responsive to this demand for these aromatic products, the art hasdeveloped a number of alternative methods to produce them in commercialquantities. One method that has been widely studied involves theselective dehydrocyclization of a dehydrocyclizable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst atdehydrocyclization conditions. As is the case with most catalyticprocedures, the principal measure of effectiveness for thisdehydrocyclization method involves the ability to perform its intendedfunction with minimum interference of side reactions for extendedperiods of time. The analytical terms used in the art to broadly measurehow well a particular catalyst performs its intended functions in aparticular hydrocarbon conversion reaction are activity, selectivity,and stability, and for purposes of discussion here, these terms aregenerally defined for a given reactant as follows: (1) activity is ameasure of the catalyst's ability to convert the hydrocarbon reactantinto products at a specified severity level where severity level meansthe specific reaction conditions used -- that is, the temperature,pressure, contact time, and presence of diluents such as H₂ ; (2)selectivity usually refers to the amount of desired product or productsobtained relative to the amount of the reactant charged or converted;(3) stability refers to the rate of change with time of the activity andselectivity parameters -- obviously the smaller rate implying the morestable catalyst. More specifically, in a dehydrocyclization process,activity commonly refers to the amount of conversion that takes placefor a given dehydrocyclizable hydrocarbon at a specified severity leveland is typically measured on the basis of disappearance of thedehydrocyclizable hydrocarbon; selectivity is typically measured by theamount, calculated on a weight percent of feed basis or on a molepercent of converted dehydrocyclizable hydrocarbon basis, of the desiredaromatic hydrocarbon or hydrocarbons obtained at the particular activityor severity level; and stability is typically equated to the rate ofchange with time of activity as measured by disappearance of thedehydrocyclizable hydrocarbon and of selectivity as measured by theamount of desired aromatic hydrocarbon produced. Accordingly, the majorproblem facing workers in the hydrocarbon dehydrocyclization orring-closure art is the development of a more active and selectivecatalytic composite that has good stability characteristics.

I have now found a dual-function acidic multimetallic catalyticcomposite which possesses improved activity, selectivity, and stabilitywhen it is employed in a process for the dehydrocyclization ofdehydrocyclizable hydrocarbons. In particular, I have determined thatthe use of an acidic multimetallic catalyst, comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, a rhenium component, and a halogen component with a porousrefractory carrier material, can enable the performance of adehydrocyclization process to be substantially improved if thecatalytically active sites induced by the metallic components areuniformly dispersed throughout the carrier material in the amounts andrelative relationships specified hereinafter and if their oxidationstates of the active metallic ingredients are carefully controlled to bein the states hereinafter specified. Moreover, particularly good resultsare obtained when this catalyst is prepared and maintained, during usein the dehydrocyclization method, in a substantially sulfur-free state.This acidic multimetallic catalytic composite is particularly useful inthe dehydrocyclization of C₆ to C₁₀ paraffins to produce aromatichydrocarbons such as benzene, toluene, and the xylenes with minimizationof byproducts such as C₁ to C₅ saturated hydrocarbons, bicyclicaromatics, olefins and coke.

In sum, the current invention involves the significant finding that acombination of a cobalt component and a rhenium component can beutilized under the circumstances specified herein to beneficiallyinteract with and promote an acidic dehydrocyclization catalystcontaining a platinum group metal when it is used in the production ofaromatics by ring-closure of aliphatic hydrocarbons.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrocyclization of dehydrocyclizablehydrocarbons utilizing an acidic multimetallic catalytic compositecomprising catalytically effective amounts of a platinum groupcomponent, a cobalt component, a rhenium component and a halogencomponent combined with a porous carier material. A second object is toprovide a novel acidic catalytic composite having superior performancecharacteristics when utilized in a dehydrocyclization process. Anotherobject is to provide an improved method for the dehydrocyclization ofparaffin hydrocarbons to produce aromatic hydrocarbons which methodminimizes undesirable byproducts such as C₁ to C₅ saturatedhydrocarbons, bicyclic aromatics, olefins and coke.

In brief summary, one embodiment of the present invention involves amethod for dehydrocyclizing a dehydrocyclizable hydrocarbon whichcomprises contacting the hydrocarbon at dehydrocyclization conditionswith an acidic multimetallic catalytic composite comprising a porouscarrier material containing a uniform dispersion of catalyticallyeffective amounts of a platinum group component, a cobalt component, arhenium component, and a halogen component. Moreover, substantially allof the platinum group component is present in the composite in theelemental metallic state and substantially all of the rhenium andcatalytically available cobalt components are present in the elementalmetallic state or in a state which is reducible to the elementalmetallic state under dehydrocyclization conditions as or a mixture ofthese states. Further these components are present in this composite inamounts, calculated on an elemental basis, sufficient to result in thecomposite containing about 0.01 to about 2 wt. % platinum group metal,about 0.1 to about 5 wt. % cobalt, about 0.01 to about 2 wt. % rheniumand about 0.1 to about 3.5 wt. % halogen.

A second embodiment relates to the dehydrocyclization method describedin the first embodiment wherein the dehydrocyclizable hydrocarbon is analiphatic hydrocarbon containing 6 to 20 carbon atoms per molecule.

A highly preferred embodiment comprehends the dehydrocyclization methodcharacterized in the first embodiment wherein the catalyst is preparedand maintained in a sulfur-free state and wherein the contacting isperformed in a substantially sulfur-free environment.

Another embodiment relates to the catalytic composite used in the first,second or third embodiments and involves the further limitation that thehalogen component is combined chloride.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrocyclizable hydrocarbons,operating conditions for use in the dehydrocyclization process, and thelike particulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention.

Regarding the dehydrocyclizable hydrocarbon that is subjected to themethod of the present invention, it can in general be any aliphatichydrocarbon or substituted aliphatic hydrocarbon capable of undergoingring-closure to produce an aromatic hydrocarbon. That is, it is intendedto include within the scope of the present invention, thedehydrocyclization of any organic compound capable of undergoing ringclosure to produce an aromatic hydrocarbon containing the same, or lessthan the same, number of carbon atoms than the reactant compound andcapable of being vaporized at the dehydrocyclization temperatures usedherein. More particularly, suitable dehydrocyclizable hydrocarbons are:aliphatic hydrocarbons containing 6 to 20 carbon atoms per molecule suchas C₆ to C₂₀ paraffins, C₆ to C₂₀ olefins and C₆ to C₂₀ polyolefins.Specific examples of suitable dehydrocyclizable hydrocarbons are: (1)paraffins such as n-hexane, 2-methylpentane, 3-methylpentane,2,2-dimethylbutane, n-heptane, 2-methylhexane, 3-ethylpentane,2,2-dimethylpentane, n-octane, 2-methylheptane, 3-ethylhexane,2,2-dimethylhexane, 2-methyl-3-ethylpentane, 2,2,3-trimethylpentane,n-nonane, 2-methyl-octane, 2,2-dimethylheptane, n-decane and the likecompounds; (2) olefins such as 1-hexene, 2-methyl-1-pentene, 1-heptene,1-octene, 1-nonene and the like compounds; and, (3) diolefins such as1,5-hexadiene, 2-methyl-2,4-hexadiene, 2,6-octadiene and the likediolefins.

In a preferred embodiment, the dehydrocyclizable hydrocarbon is aparaffin hydrocarbon having about 6 to 10 carbon atoms per molecule. Forexample, paraffin hydrocarbons containing about 6 to 8 carbon atoms permolecule are dehydrocyclized by the subject method to produce thecorresponding aromatic hydrocarbon. It is to be understood that thespecific dehydrocyclizable hydrocarbons mentioned above can be chargedto the present method individually, in admixture with one or more of theother dehydrocyclizable hydrocarbons, or in admixture with otherhydrocarbons such as naphthenes, aromatics, C₁ to C₅ paraffins and thelike. Thus mixed hydrocarbon fractions, containing significantquantities of dehydrocyclizable hydrocarbons that are commonly availablein a typical refinery, are suitable charge stocks for the instantmethod; for example, highly paraffinic straight run naphthas, paraffinicraffinates from aromatic extraction or adsorption, C₆ to C₉paraffin-rich streams and the like refinery streams. Generally, bestresults are obtained with a charge stock comprising a mixture of C₆ toC₉ paraffins, and especially C₆ to C₉ normal paraffins.

The acidic multimetallic catalyst used in the present dehydrocyclizationmethod comprises a porous carrier material having combined therewithcatalytically effective amounts of a platinum group component, a cobaltcomponent, a rhenium component, and a halogen component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high-surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon conversion process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts such as: (1) activated carbon, coke, orcharcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc., (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, MnAl₂ O₄, CaAl₂ O₄, and other like compounds having theformula MO.sup.. Al₂ O₃ where M is a metal having a valence of 2; and(7) combinations of elements from one or more of these groups. Thepreferred porous carrier materials for use in the present invention arerefractory inorganic oxides, with best results obtained with an aluminacarrier material. Suitable alumina materials are the crystallinealuminas known as gamma-, eta-, and theta-alumina, with gamma- oreta-alumina giving best results. In addition, in some embodiments thealumina carrier material may contain minor proportions of other wellknown refractory inorganic oxides such as silica, zirconia, magnesia,etc.; however, the preferred support is substantially pure gamma- oreta-alumina. Preferred carrier materials have an apparent bulk densityof about 0.3 to about 0.8 g/cc and surface area characteristics suchthat the average pore diameter is about 20 to 300 Angstroms, the porevolume is about 0.1 to about 1 cc/g and the surface area is about 100 toabout 500 m² /g. In general, best results are typically obtained with agamma-alumina carrier material which is used in the form of sphericalparticles having: a relatively small diameter (i.e., typically about1/16 inch), an apparent bulk density of about 0.3 to about 0.8 g/cc, apore volume of about 0.4 ml/g, and a surface area of about 150 to about250 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere, and alumina spheres may becontinuously manufactured by the well-known oil drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting aluminum metal with hydrochloricacid, combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° toabout 400° F. and subjected to a calcination procedure at a temperatureof about 850° to about 1300° F. for a period of about 1 to about 20hours. This treatment effects conversion of the alumina hydrogel to thecorresponding crystalline gamma-alumina. See the teachings of U.S. Pat.No. 2,620,314 for additional details.

As used herein, the expression "catalytically available cobalt" isintended to mean the portion of the cobalt component of the subjectcatalytic composite that is available for use in accelerating thedehydrocyclization reaction of interest. For purposes of the presentinvention, it is highly preferred that the catalytically availablecobalt comprise at least about 10% of the total cobalt content of thecatalyst and, ever more preferably, at least about 50% thereof. Forcertain types of carrier materials which can be used in the preparationof the instant catalyst composite, it has been observed that a portionof the cobalt incorporated therein is essentially bound-up in thecrystal structure thereof in a manner which essentially makes itcatalytically unavailable; in fact, it is more a part of the refractorycarrier material than a catalytically active component. Specificexamples of this effect are observed when the carrier material can forma refractory spinel or spinel-like structure with a portion of thecobalt component and/or when a refractory cobalt oxide or aluminate isformed by reaction of the carrier material (or precursors thereof) witha portion of the cobalt component. When this effect occurs, it is onlywith great difficulty that the portion of the cobalt bound-up with thesupport can be reduced to a catalytically active state and theconditions required to do this are beyond the severity levels normallyassociated with hydrocarbon conversion conditions and are in fact likelyto seriously damage the necessary porous characteristics of the support.In the cases where cobalt can interact with the crystal structure of thesupport to render a portion thereof catalytically unavailable, theconcept of the present invention merely requires that the amount ofcobalt added to the subject catalyst be adjusted to satisfy therequirements of the support as well as the catalytically availablecobalt requirements of the present invention. Against this backgroundthen, the hereinafter stated specifications for oxidation state anddispersion of the cobalt component are to be interpreted as directed toa description of the catalytically available cobalt. On the other hand,the specifications for the amount of cobalt used are to be interpretedto include all of the cobalt contained in the catalyst in any form.

One essential ingredient of the present catalytic composite is a rheniumcomponent. It is of fundamental importance that substantially all of therhenium component exists within the catalytic composite of the presentinvention in the elemental metallic state or in a state which isreducible to the elemental metallic state under hydrocarbon conversionconditions or in a mixture of these states. The rhenium component may beutilized in the composite in any amount which is catalyticallyeffective, with the preferred amount being about 0.01 to about 2 wt. %thereof, calculated on an elemental basis. Typically, best results areobtained with about 0.05 to about 1 wt. % rhenium. It is additionallypreferred to select the specified amount of rhenium from within thisbroad weight range as a function of the amount of the platinum groupcomponent, on an atomic basis, as is explained hereinafter.

This rhenium component may be incorporated into the catalytic compositein any suitable manner known to those skilled in the catalystformulation art which results in a relatively uniform distribution ofrhenium in the carrier material such as by coprecipitation,ion-exchange, or impregnation. In addition, it may be added at any stageof the preparation of the composite -- either during preparation of thecarrier material or thereafter -- and the precise method ofincorporation used is not deemed to be critical. However, best resultsare obtained when the rhenium component is relatively uniformlydistributed throughout the carrier material in a relatively smallparticle size, and the preferred procedures are the ones known to resultin a composite having this relatively uniform distribution. Oneacceptable procedure for incorporating this component into the compositeinvolves cogelling or coprecipitating the rhenium component during thepreparation of the preferred carrier material, alumina. This procedureusually comprehends the addition of a soluble, decomposable compound ofrhenium such as perrhenic acid or a salt thereof to the alumina hydrosolbefore it is gelled. The resulting mixture is then finished byconventional gelling, aging, drying, and calcination steps as explainedhereinbefore. A preferred way of incorporating this component is animpregnation step wherein the porous carrier material is impregnatedwith a suitable rhenium-containing solution either before, during, orafter the carrier material is calcined. Preferred impregnation solutionsare aqueous solutions of water soluble, decomposable rhenium compoundssuch as ammonium perrhenate, sodium perrhenate, potassium perrhenate,potassium rhenium oxychloride (K₂ ReOCl₅), potassium hexachlororhenate(IV), rhenium chloride, rhenium heptoxide, and the like compounds. Bestresults are ordinarily obtained when the impregnation solution is anaqueous solution of perrhenic acid. This component can be added to thecarrier material either prior to, simultaneously with, or after theother metallic components are combined therewith. Best results areusually achieved when this component is added simultaneously with theother metallic components. In fact, excellent results are obtained witha one step impregnation procedure using an acidic aqueous solutioncontaining chloroplatinic acid, perrhenic acid, cobaltous chloride, andhydrochloric acid.

A second essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof, asa second component of the present composite. It is an essential featureof the present invention that substantially all of this platinum groupcomponent exists within the final catalytic composite in the elementalmetallic state. Generally, the amount of this component present in thefinal catalytic composite is small compared to the quantities of theother components combined therewith. In fact, the platinum groupcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum, iridium, rhodium, or palladium metal. Particularlypreferred mixtures of these metals are platinum and iridium, andplatinum and rhodium.

This platinum group component may be incorporated in the catalyticcomposite in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of a platinum, iridium, rhodium,or palladium chloride compound, such as chloropaltinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is preferred sinceit facilitates the incorporation of both the platinum group componentsand at least a minor quantity of the halogen component in a single step.Hydrogen chloride or the like acid is also generally added to theimpregnation solution in order to further facilitate the incorporationof the halogen component and the uniform distribution of the metalliccomponents throughout the carrier material. In addition, it is generallypreferred to impregnate the carrier material after it has been calcinedin order to minimize the risk of washing away the valuable platinum orpalladium compounds; however, in some cases it may be advantageous toimpregnate the carrier material when it is in a gelled state.

A third essential ingredient of the acidic multimetallic catalyticcomposite used in the present invention is a cobalt component. Althoughthis component may be initially incorporated into the composite in manydifferent decomposable forms which are hereinafter stated, my basicfinding is that the catalytically active state for hydrocarbonconversion with this component is the elemental metallic state.Consequently, it is a feature of my invention that substantially all ofthe catalytically available cobalt component exists in the catalyticcomposite either in the elemental metallic state or in a state which isreducible to the elemental state under hydrocarbon conversion conditionsor in a mixture of these states. Examples of this last state areobtained when the catalytically available cobalt component is initiallypresent in the form of cobalt oxide, hydroxide, halide, oxyhalide, andthe like reducible compounds. As a corollary to this basic finding onthe active state of the catalytically available cobalt component, itfollows that the presence of the catalytically available cobalt in formswhich are not reducible at hydrocarbon conversion conditions is to bescrupulously avoided if the full benefits of the present invention areto be realized. Illustrative of these undesired forms are cobalt sulfideand the cobalt oxysulfur compounds such as cobalt sulfate. Best resultsare obtained when the composite initially contains all of thecatalytically available cobalt component in the elemental metallic stateor in a reducible oxide state or in a mixture of these states. Allavailable evidence indicates that the preferred preparation procedurespecifically described in Example I results in a catalyst having thecatalytically available cobalt component in a reducible oxide form.Based on the performance of such a catalyst, it is believed thatsubstantially all of this reducible oxide form of the cobalt componentis reduced to the elemental metallic state when a hydrocarbon conversionprocess (such as dehydrocyclization) using this catalyst is started-upand lined-out at hydrocarbon conversion conditions. The cobalt componentmay be utilized in the composite in any amount which is catalyticallyeffective, with the preferred amount being about 0.1 to about 5 wt. %thereof, calculated on an elemental cobalt basis. Typically, bestresults are obtained with about 0.25 to about 2.5 wt. % cobalt. It is,additionally, preferred to select the specific amount of cobalt fromwithin this broad weight range as a function of the amount of theplatinum group component, on an atomic basis, as is explainedhereinafter.

The cobalt component may be incorporated into the catalytic composite inany suitable manner known to those skilled in the catalyst formulationart to result in a relatively uniform distribution of the catalyticallyavailable cobalt in the carrier material such as coprecipitation,cogelation, ion exchange, impregnation, etc. In addition, it may beadded at any stage of the preparation of the composite -- either duringpreparation of the carrier material or thereafter -- since the precisemethod of incorporation used is not deemed to be critical. However, bestresults are obtained when the catalytically available cobalt componentis relatively uniformly distributed throughout the carrier material in arelatively small particle or crystallite size having a maximum dimensionof less than 100 Angstroms, and the preferred procedures are the onesthat are known to result in a composite having a relatively uniformdistribution of the catalytically available cobalt moiety in arelatively small particle size. One acceptable procedure forincorporating this component into the composite involves cogelling orcoprecipitating the cobalt component during the preparation of thepreferred carrier material, alumina. This procedure usually comprehendsthe addition of a soluble, decomposable, and reducible compound ofcobalt such as cobalt chloride or nitrate to the alumina hydrosol beforeit is gelled. Alternatively, the reducible compound of cobalt can beadded to the gelling agent before it is added to the hydrosol. Theresulting mixture is then finished by conventional gelling, aging,drying, and calcination steps as explained hereinbefore. One preferredway of incorporating this component is an impregnation step wherein theporous carrier material is impregnated with a suitable cobalt-containingsolution either before, during, or after the carrier material iscalcined or oxidized. The solvent used to form the impregnation solutionmay be water, alcohol, ether, or any other suitable organic or inorganicsolvent provided the solvent does not adversely interact with any of theother ingredients of the composite or interfere with the distributionand reduction of the cobalt component. Preferred impregnation solutionsare aqueous solutions of water-soluble, decomposable, and reduciblecobalt compounds such as cobaltous acetate, cobaltous benzoate,cobaltous bromate, cobaltous bromide, cobaltous chlorate andperchlorate, cobaltous chloride, cobaltic chloride, cobaltous fluoride,cobaltous iodide, cobaltous nitrate, hexamminecobalt (III) chloride,hexamminecobalt (III) nitrate, triethylenediamminecobalt (III) chloride,cobaltous hexamethylenetetramine, and the like compounds. Best resultsare ordinarily obtained when the impregnation solution is an aqueoussolution of cobalt chloride or cobalt nitrate. This cobalt component canbe added to the carrier material, either prior to, simultaneously with,or after the other metallic components are combined therewith. Bestresults are usually achieved when this component is added simultaneouslywith the platinum group and rhenium components via an acidic aqueousimpregnation solution. In fact, excellent results are obtained, asreported in the examples, with an impregnation procedure using an acidicaqueous solution comprising chloroplatinic acid, perrhenic acid,cobaltous chloride, and hydrochloric acid.

It is essential to incorporate a halogen component into the acidicmultimetallic catalytic composite used in the present invention.Although the precise form of the chemistry of the association of thehalogen component with the carrier material is not entirely known, it iscustomary in the art to refer to the halogen component as being combinedwith the carrier material, or with the other ingredients of the catalystin the form of the halide (e.g., as the chloride). This combined halogenmay be either fluorine, chlorine, iodine, bromine, or mixtures thereof.Of these, fluorine and, particularly, chlorine are preferred for thepurposes of the present invention. The halogen may be added to thecarrier material in any suitable manner, either during preparation ofthe support or before or after the addition of the other components. Forexample, the halogen may be added, at any stage of the preparation ofthe carrier material or to the calcined carrier material, as an aqueoussolution of a suitable, decomposable halogen-containing compound such ashydrogen fluoride, hydrogen chloride, hydrogen bromide, ammoniumchloride, etc. The halogen component or a portion thereof, may becombined with the carrier material during the impregnation of the latterwith the platinum group, cobalt, or rhenium components; for example,through the utilization of a mixture of chloroplatinic acid and hydrogenchloride. In another situation, the alumina hydrosol which is typicallyutilized to form the preferred alumina carrier material may containhalogen and then contribute at least a portion of the halogen componentto the final composite. For the dehydrocyclization reaction, the halogenwill be typically combined with the carrier material in an amountsufficient to result in a final composite that contains about 0.1 toabout 3.5%, and preferably about 0.5 to about 1.5%, by weight ofhalogen, calculated on an elemental basis. It is to be understood thatthe specified level of halogen component in the instant catalyst can beachieved or maintained during use in the dehydrocyclization ofhydrocarbons by continuously or periodically adding to the reaction zonea decomposable halogen-containing compound such as an organic chloride(e.g., ethylene dichloride, carbon tetrachloride, t-butyl chloride) inan amount of about 1 to 100 wt. ppm. of the hydrocarbon feed, andpreferably, about 1 to 10 wt. ppm.

Regarding especially preferred amounts of the various metalliccomponents of the subject catalyst, I have found it to be an excellentpractice to specify the amounts of the cobalt components and the rheniumcomponent as a function of the amount of the platinum group component.On this basis, the amount of the cobalt component is ordinarily selectedso that the atomic ratio of cobalt to platinum group metal contained inthe composite is about 0.2:1 to about 66:1, with the preferred rangebeing about 0.8:1 to about 18:1. Similarly, the amount of the rheniumcomponent is ordinarily selected to produce a composite containing anatomic ratio of rhenium to platinum group metal of about 0.05:1 to about10:1, with the preferred range being about 0.2:1 to about 5:1.

Another significant parameter for the instant catalyst is the "totalmetals content" which is defined to be the sum of the platinum groupcomponent, the cobalt component, and the rhenium component, calculatedon an elemental basis. Good results are ordinarily obtained with thesubject catalyst when this parameter is fixed at a value of about 0.15to about 4 wt. %, with best results ordinarily achieved at a metalsloading of about 0.3 to about 3 wt. %.

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the final catalyst generallywill be dried at a temperature of about 200° to about 600° F. for aperiod of at least about 2 to about 24 hours or more, and finallycalcined or oxidized at a temperature of about 700° to about 1100° F. inan air to oxygen atmosphere for a period of about 0.5 to about 10 hoursin order to convert substantially all of the metallic components to thecorresponding oxide form. Because a halogen component is utilized in thecatalyst, best results are generally obtained when the halogen contentof the catalyst is adjusted during the oxidation step by including ahalogen or a halogen-containing compound such as HCl or an HCl-producingsubstance in the air or oxygen atmosphere utilized. In particular, whenthe halogen component of the catalyst is chlorine, it is preferred touse a mole ratio of H₂ O to HCl of about 5:1 to about 100:1 during atleast a portion of the oxidation step in order to adjust the finalchlorine content of the catalyst to a range of about 0.1 to about 3.5wt. %. Preferably, the duration of this halogenation step is about 1 to5 hours.

The resultant oxidized catalytic composite is preferably subjected to asubstantially water-free and hydrocarbon-free reduction step prior toits use in the conversion of hydrocarbons. This step is designed toselectively reduce at least the platinum group component to theelemental metallic state and to insure a uniform and finely divideddispersion of the metallic components throughout the carrier material.Preferably substantially pure and dry hydrogen (i.e., less than 20 vol.ppm. H₂ O) is used as the reducing agent in this step. The reducingagent is contacted with the oxidized catalyst at conditions including areduction temperature of about 400° to about 1200° F. and a period oftime of about 0.5 to 10 hours effective to at least reduce substantiallyall of the platinum group component to the elemental metallic state.Quite surprisingly, it has been found that if this reduction step isperformed with a hydrocarbon-free hydrogen stream at the temperatureindicated, and if the catalytically available cobalt component isproperly distributed in the carrier material in the oxide form and inthe specified particle size, no substantial amount of the catalyticallyavailable cobalt component will be reduced in this step. However, oncethe catalyst sees a mixture of hydrogen and hydrocarbon (such as duringthe starting-up and lining-out of the dehydrocyclization process usingsame), substantially all of the catalytically available cobalt componentis quickly reduced at the specified reduction temperature range. Thisreduction treatment may be performed in situ as part of a start-upsequence if precautions are taken to predry the plant to a substantiallywater-free state and if substantially water-free and hydrocarbon-freehydrogen is used.

The resulting reduced catalytic composite is, in accordance with thebasic concept of the present invention, preferably maintained in asulfur-free state both during its preparation and thereafter during itsuse in the dehydrocyclization of hydrocarbons. As indicated previously,the beneficial interaction of the catalytically available cobaltcomponent with the other ingredients of the present catalytic compositeis contingent upon the maintenance of the cobalt moiety in a highlydispersed, readily reducible state in the carrier material. Sulfur inthe form of sulfide adversely interferes with both the dispersion andreducibility of the catalytically available cobalt component andconsequently it is a highly preferred practice to avoid presulfiding theselectively reduced acidic multimetallic catalyst resulting from thereduction step. Once the catalyst has been exposed to hydrocarbon for asufficient period of time to lay down a protective layer of carbon orcoke on the surface thereof, the sulfur sensitivity of the resultingcarbon-containing composite changes rather markedly and the presence ofsmall amounts of sulfur can be tolerated without permanently disablingthe catalyst. The exposure of the freshly reduced catalyst to sulfur canseriously damage the cobalt component thereof and consequently,jeopardize the superior performance characteristics associatedtherewith. However, once a protective layer of carbon is established onthe catalyst, the sulfur deactivation effect is less permanent andsulfur can be purged therefrom by exposure to a sulfur-free hydrogenstream at a temperature of about 800° to 1100° F.

According to the present invention, the dehydrocyclizable hydrocarbon iscontacted with the instant acidic multimetallic catalyst in adehydrocyclization zone maintained at dehydrocyclization conditions.This contacting may be accomplished by using a catalyst in a fixed bedsystem, a moving bed system, a fluidized bed system, or in a batch typeoperation; however, in view of the danger of attrition losses of thevaluable catalyst and of well known operational advantages, it ispreferred to use either a fixed bed system or a dense-phase moving bedsystem such as is shown in U.S. Pat. No. 3,725,249. It is alsocontemplated that the contacting step can be performed in the presenceof a physical mixture of particles of the catalyst of the presentinvention and particles of a conventional dual-function catalyst of theprior art. In a fixed bed system, the dehydrocyclizablehydrocarbon-containing charge stock is preheated by any suitable heatingmeans to the desired reaction temperature and then passed into adehydrocyclization zone containing a fixed bed of the acidicmultimetallic catalyst. It is of course, understood that thedehydrocyclization zone may be one or more separate reactors withsuitable means therebetween to ensure that the desired conversiontemperature is maintained at the entrance to each reactor. It is alsoimportant to note that the reactants may be contacted with the catalystbed in either upward, downward, or radial flow fashion with the latterbeing preferred. In addition, the reactants may be in the liquid phase,a mixed liquid-vapor phase, or a vapor phase when they contact thecatalyst, with best results obtained in the vapor phase. Thedehydrocyclization system then preferably comprises a dehydrocyclizationzone containing one or more fixed beds or dense-phase moving beds of theinstant catalyst. In a multiple bed system, it is, of course, within thescope of the present invention to use the present catalyst in less thanall of the beds with a conventional dual-function catalyst being used inthe remainder of the beds. This dehydrocylization zone may be one ormore separate reactors with suitable heating means therebetween tocompensate for the endothermic nature of the dehydrocylization reactionthat takes place in each catalyst bed.

Although hydrogen is the preferred diluent for use in the subjectdehydrocyclization method, in some cases other art-recognized diluentsmay be advantageously utilized, either individually or in admixture withhydrogen, such as C₁ to C₅ paraffins such as methane, ethane, propane,butane and pentane; carbon dioxide, the like diluents, and mixturesthereof. Hydrogen is preferred because it serves the dual-function ofnot only lowering the partial pressure of the dehydrocyclizablehydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits (commonly called coke) on thecatalytic composite. Ordinarily, hydrogen is utilized in amountssufficient to insure a hydrogen to hydrocarbon mole ratio of about 0.1:1to about 10:1, with best results obtained in the range of about 0.5:1 toabout 5:1. The hydrogen stream charged to the dehydrocyclization zonewill typically be recycle hydrogen obtained from the effluent streamfrom this zone after a suitable hydrogen separation step.

Since sulfur has a high affinity for cobalt at dehydrocyclizationconditions, I have found that best results are achieved in adehydrocyclization method using the instant acidic multimetalliccatalytic composite when the catalyst is used in a substantiallysulfur-free environment. The expression "substantially sulfur-freeenvironment" is intended to mean that the total amount (expressed asequivalent elemental sulfur) of sulfur or sulfur-containing compounds,which are capable of producing a metallic sulfide at the reactionconditions used, entering the dehydrocyclization zone containing theinstant catalyst from any source is continuously maintained at an amountequivalent to less than 10 wt. ppm. of the hydrocarbon charge stock,more preferably less than 5 wt. ppm., and most preferably less than 1wt. ppm. Since in the ordinary operation of the subjectdehydrocyclization method the influent hydrogen stream is autogenouslyproduced, the prime source for any sulfur entering thedehydrocyclization zone is the hydrocarbon charge stock, maintaining thecharge stock substantially free of sulfur is ordinarily sufficient toensure that the environment containing the catalyst is maintained in thesubstantially sulfur-free state. More specifically, since hydrogen is amajor product of the dehydrocyclization process, ordinarily the inputdiluent stream required for the process is obtained by recycling aportion of the hydrogen-rich stream recovered from the effluentwithdrawn from the dehydrocylization zone. In this typical situation,this recycle hydrogen stream will ordinarily be substantially free ofsulfur if the charge stock is maintained free of sulfur. If autogenoushydrogen is not utilized as the diluent, then, of course, the concept ofthe present invention requires that the input diluent stream bemaintained substantially sulfur-free; that is, less than 10 vol. ppm. ofH₂ S, preferably less than 5 vol. ppm., and most preferably less than 1vol. ppm.

The only other possible sources of sulfur that could interfere with theperformance of the instant catalyst are sulfur that is initiallycombined with the catalyst and/or with the plant hardware. As indicatedhereinbefore, a highly preferred feature of the present acidicmulti-metallic catalyst is that it is maintained in a substantiallysulfur-free state; therefore, sulfur released from the catalyst is notusually a problem in the present process. Hardware sulfur is ordinarilynot present in a new plant; it only becomes a problem when the presentprocess is to be implemented in a plant that has seen service with asulfur-containing feedstream. In this latter case, the preferredpractice of the present invention involves an initial pretreatment ofthe sulfur-containing plant in order to remove substantially all of thedecomposable hardware sulfur therefrom. This can be easily accomplishedby any of the techniques for stripping sulfur from hardware known tothose in the art; for example, by the circulation of a substantiallysulfur-free hydrogen stream through the internals of the plant at arelatively high temperature of about 800° to about 1200° F. until the H₂S content of the effluent gas stream drops to a relatively low level --typically less than 5 vol. ppm. and preferably less than 2 vol. ppm. Insum, the preferred sulfur-free feature of the present invention requiresthat the total amount of detrimental sulfur entering thedehydrocyclization zone containing the hereinbefore described acidicmultimetallic catalyst must be continuously maintained at asubstantially low level; specifically, the amount of sulfur must be heldto a level equivalent to less than 10 wt. ppm., and preferably less than1 wt. ppm., of the feed.

In the case where the sulfur content of the charge stock for the presentprocess is greater than the amounts previously specified, it is, ofcourse, necessary to treat the charge stock in order to remove theundesired sulfur contaminants therefrom. This is easily accomplished byusing any one of the conventional catalytic pretreatment methods such ashydrorefining, hydrotreating, hydrodesulfurization, and the like toremove substantially all sulfurous, nitrogenous, and water-yieldingcontaminants from this feedstream. Ordinarily, this involves subjectingthe sulfur-containing feedstream to contact with a suitablesulfur-resistant hydrorefining catalyst in the presence of hydrogenunder conversion conditions selected to decompose sulfur contaminantscontained therein and form hydrogen sulfide. The hydrorefining catalysttypically comprises one or more of the oxides or sulfides of thetransition metals of Groups VI and VIII of the Periodic Table. Aparticularly preferred hydrorefining catalyst comprises a combination ofa metallic component from the iron group metals of Group VIII and of ametallic component of the Group VI transition metals combined with asuitable porous refractory support. Particularly good results have beenobtained when the iron group component is cobalt and/or nickel and theGroup VI transition metal is molybdenum or tungsten. The preferredsupport for this type of catalyst is a refractory inorganic oxide of thetype previously mentioned. For example, good results are obtained with ahydrorefining catalyst comprising cobalt oxide and molybdenum oxidesupported on a carrier material comprising alumina and silica. Theconditions utilized in this hydrorefining step are ordinarily selectedfrom the following ranges: a temperature of about 600° to about 950° F.,a pressure of about 500 to about 5000 psig., a liquid hourly spacevelocity of about 1 to about 20 hr.⁻ ¹, and a hydrogen circulation rateof about 500 to about 10,000 standard cubic feet of hydrogen per barrelof charge. After this hydrorefining step, the hydrogen sulfide, ammonia,and water liberated therein, are then easily removed from the resultingpurified charge stock by conventional means such as a suitable strippingoperation. Specific hydro-refining conditions are selected from theranges given above as a function of the amounts and kinds of the sulfurcontaminants in the feedstream in order to produce a substantiallysulfur-free charge stock which is then charged to a process of thepresent invention.

It is also generally preferred to utilize the novel acidic multimetalliccatalytic composite in a substantially water-free environment. Essentialto the achievement of this condition in the dehydrocyclization zone isthe control of the water level present in the charge stock and thediluent stream which is being charged to the zone. Best results areordinarily obtained when the total amount of water entering theconversion zone from any source is held to a level less than 20 ppm. andpreferably less than 5 ppm. expressed as weight of equivalent water inthe charge stock. In general, this can be accomplished by carefulcontrol of the water present in the charge stock and in the diluentstream. The charge stock can be dried by using any suitable drying meansknown to the art, such as a conventional solid adsorbent having a highselectivity for water, for instance, sodium or calcium crystallinealuminosilicates, silica gel, activated alumina, molecular sieves,anhydrous calcium sulfate, high surface area sodium, and the likeabsorbents. Similarly, the water content of the charge stock may beadjusted by suitable stripping operations in a fractionation column orlike device. And in some cases, a combination of adsorbent drying anddistillation drying may be used advantageously to effect almost completeremoval of water from the charge stock. In an especially preferred modeof operation, the charge stock is dried to a level corresponding to lessthan 5 wt. ppm. of H₂ O equivalent. In general, it is preferred tomaintain the diluent stream entering the hydrocarbon conversion zone ata level of about 10 vol. ppm. of water or less and most preferably about5 vol. ppm. or less. If the water level in the diluent stream is toohigh, drying of same can be conveniently accomplished by contacting thisstream with a suitable desiccant such as those mentioned above.

The dehydrocylization conditions used in the present method include areactor pressure which is selected from the range of about 0 psig. toabout 250 psig., with the preferred pressure being about 50 psig. toabout 150 psig. In fact, it is a singular advantage of the presentinvention that it allows stable operation at lower pressure than haveheretofore been successfully utilized in dehydrocyclization system withall platinum monometallic catalysts. In other words, the acidicmulti-metallic catalyst of the present invention allows the operation ofa dehydrocyclization system to be conducted at lower pressure for aboutthe same or better catalyst cycle life before regeneration as has beenheretofore realized with conventional monometallic catalysts at higherpressure.

The temperature required for dehydrocyclization with the instantcatalyst is markedly lower than that for a similar operation using ahigh quality catalyst of the prior art. This significant and desirablefeature of the present invention is a consequence of the extraordinaryactivity of the acidic multimetallic catalyst of the present inventionfor the dehydrocyclization reaction. Hence, the present inventionrequires a temperature in the range of from 800° to about 1100° f. andpreferably about 850° to about 1000° F. As is well known to thoseskilled in the dehydrocyclization art, the initial selection of thetemperature within this broad range is made primarily as a function ofthe desired conversion level of the dehydrocylizable hydrocarbonconsidering the characteristics of the charge stock and of the catalyst.Ordinarily, the temperature then is thereafter slowly increased duringthe run to compensate for the inevitable deactivation that occurs toprovide a relatively constant value for conversion. Therefore, it is afeature of the present invention that not only is the initialtemperature requirement substantially lower, but also the rate at whichthe temperature is increased in order to maintain a constant conversionlevel is substantially lower for the catalyst of the present inventionthan for an equivalent operation with a high quality dehydrocyclizationcatalyst which is manufactured in exactly the same manner as thecatalyst of the present invention except for the inclusion of the cobaltand rhenium components. Moreover, for the catalyst of the presentinvention, the aromatic yield loss for a given temperature increase issubstantially lower than for a high quality dehydrocyclization catalystof the prior art.

The liquid hourly space velocity (LHSV) used in the instantdehydrocyclizaton method is selected from the range of about 0.1 toabout 5 hr..sup.⁻¹, with a value in the range of about 0.3 to about 2hr..sup.⁻¹ being preferred. In fact, it is a feature of the presentinvention that it allows operations to be conducted at higher LHSV thannormally can be stably achieved in a dehydrocyclizaton process with ahigh quality dehydrocyclizaton catalyst of the prior art. This lastfeature is of immense economic significance because it allows adehydrocylization process to operate at the same throughput level withless catalyst inventory or at greatly increased throughput level withthe same catalyst inventory than that heretofore used with conventionaldehydrocyclization catalysts at no sacrifice in catalyst life beforeregeneration.

The following working examples are given to illustrate further thepreparation of the acidic multimetallic catalytic composite used in thepresent invention and the beneficial use thereof in thedehydrocyclization of hydrocarbons. It is understood that the examplesare intended to be illustrative rather than restrictive.

These examples are all performed in a laboratory scaledehydrocyclization plant comprising a reactor, a hydrogen separatingzone, heating means, cooling means, pumping means, compressing means,and the like conventional equipment. In this plant, a sulfur-free feedstream containing the dehydrocyclizable hydrocarbon is combined with ahydrogen recycle stream and the resultant mixture heated to the desiredconversion temperature, which refers herein to the temperaturemaintained at the inlet to the reactor. The heated mixture is thenpassed into contact with the instant acidic multimetallic catalyst whichis maintained in a sulfur-free and water-free environment and which ispresent as a fixed bed of catalyst particles in the reactor. Thepressures reported herein are recorded at the outlet from the reactor.An effluent stream is withdrawn from the reactor, cooled, and passedinto the hydrogen-separating zone wherein a hydrogen-containing gasphase separates from a hydrocarbonrich liquid phase containing aromatichydrocarbons, unconverted dehydrocyclizable hydrocarbons, and byproductsof the dehydrocyclization reaction. A portion of the hydrogen-containinggas phase is recovered as excess recycle gas and the remaining portionis passed through a high surface area sodium scrubber and the resultingsubstantially water-free and sulfur-free hydrogen stream is recycledthrough suitable compressing means to the heating zone as describedabove. The hydrogen-rich liquid phase from the separating zone iswithdrawn therefrom and subjected to analysis to determine conversionand selectively for the desired aromatic hydrocarbon as will beindicatedin the Examples. Conversion numbers of the dehydrocyclizablehydrocarbon reported hrein are all calculated on the basis ofdisappearance of the dehydrocyclizable hydrocarbon and are expressed inweight percent. Similarly, selectivity numbers are reported on the basisof weight of desired aromatic hydrocarbon produced per 100 weight partsof dehydrocyclizable hydrocarbon charged.

All of the catalysts utilized in these examples are prepared accordingto the following general method with suitable modification instoichiometry to achieve the compositions reported in each example.First, an alumina carrier material comprising 1/16 inch spheres havingan apparent bulk density of about 0.5 g/cc is prepared by: forming analuminum hydroxyl chloride sol by dissolving substantially pure aluminumpellets in a hydrochloric acid solution, adding hexamethylenetetramineto the resulting alumina sol, gelling the resulting solution by droppingit into an oil bath to form spherical particles of an alumina hydrogel;aging, and washing the resulting particles with an ammonical solutionand finally drying and calcining the aged and washed particles to formsphereical particles of gamma-alumina containing about 0.3 wt. %combined chloride. Additional details as to this method of preparingthis alumina carrier material are given in the teachings of U.S. Pat.No. 2,620,314.

The resulting gamma-alumina particles are then contacted at suitableimpregnation conditions with an aqueous impregnation solution containingchloroplatinic acid, perrhenic acid, cobaltous chloride and hydrogenchloride. The amounts of metallic reagents contained in thisimpregnation solution are carefully adjusted to yield a finalmultimetallic catalytic composite containing a uniform dispersion of thedesired amounts of platinum, rhenium, and cobalt. The hydrochloric acidis utilized in an amount of about 3 wt. % of the alumina particles. Inorder to ensure a uniform dispersion of the metal moieties in thecarrier material, the impregnation solution is maintained in contactwith the carrier material particles for about to about 3 hours at atemperature of about 70° F. with constant agitation. The impregnatedspheres are then dried at a temperature of about 225° F. for about anhour and thereafter calcined or oxidized with a sulfur-free dry airstream at a temperature of about 975° F. and a GHSV of about 500hr..sup.⁻¹ for about 1/2hour effective to convert substantially all ofthe metallic components to the corresponding oxide forms. In general, itis a good practice to thereafter treat the resulting oxidized particleswith a sulfur-free air stream containing H₂ O and HCl in a mole ratio ofabout 30:1 at a temperature of about 975° F. for an additional period ofabout 2 hours in order to adjust the combined chloride contained in thecatalyst to a value of about 1 wt. % The halogen-treated spheres arenext subjected to a second oxidation step with a dry sulfur-free airstream at 975° F. and a GHSV of 500 hr..sup.⁻¹ for an additional periodof about 1/2 hour. The resulting oxidized and halogen-treated particlesare thereafter subjected to dry prereduction treatment designed, aspointed out hereinbefore, to reduce at least substantially all of theplatinum component to the elemental metallic state. This step involvescontacting the catalyst particles with a substantially sulfur-free andhydrocarbon-free hydrogen stream containing less than 5 vol. ppm. of H₂O at a temperature of 1050° F., atmospheric pressure and a GHSV of about400 hr..sup.⁻¹ for a period of about 1 hour.

EXAMPLE I

The reactor is loaded with 100 cc of an acidic catalyst containing, onan elemental basis, 0.375 wt. % platinum, 0.5 wt. % cobalt, and 0.375wt. % rhenium, and about 1 wt. % chloride. The feed stream utilized iscommercial grade n-hexane. The feed stream is contacted with thecatalyst at a temperature of 920° F., a pressure of 125 psig., a liquidhourly space velocity of 0.75 hr..sup.⁻¹, and a hydrogen to hydrocarbonmole ratio of 3:1. The dehydrocyclization plant is lined-out at theseconditions and a 20 hour test period commenced. The hydrocarbon productstream from the plant is continuously analyzed by GLC (gas liquidchromatography) and about a 90% conversion of n-hexane is observed witha selectivity for benzene of about 25%.

EXAMPLE II

The acidic catalyst contains, on an elemental basis, 0.375 wt. %platinum, 0.5 wt. % cobalt, 0.2 wt. % rhenium and 1 wt. % combinedchloride. The feed stream is commercial grade normal heptane. Thedehydrocyclization reactor is operated at a temperature of 900° F., apressure of 125 psig., a liquid hourly space velocity of 0.75hr..sup.⁻¹, and a hydrogen to hydrocarbon mole ratio of 3:1. After aline-out period, a 20 hour test period is performed during which theaverage conversion of the n-heptane is maintained at about 95% with aselectivity for aromatics (a mixture of toluene and benzene) of about45%.

EXAMPLE III

The acidic catalyst is the same as utilized in Example II. The feedstream is normal octane. the conditions utilized are a temperature of880° F., a pressure of 125 psig., a liquid hourly space velocity of 0.75hr..sup.⁻¹, and a hydrogen to hydrocarbon mole ratio of 3:1. After aline-out period a 20 hour test shows an average conversion of about 100%and a selectivity for aromatics of about 50%.

EXAMPLE IV

The acidic catalyst contains, on an elemental basis, 0.3 wt. % platinum,1.0 wt. % cobalt, 0.2 wt. % rhenium and 1.0 wt. % combined chloride. Thefeed stream is a 50/50 mixture of n-hexane and n-heptane. The conditionsutilized are a temperature of 945° F., a pressure of 125 psig., a liquidhourly space velocity of 0.75 hr..sup.⁻¹, and a hydrogen to hydrocarbonmole ratio of 2:1. After a line-out period, a 20 hour test is performedwith a conversion of about 100% and a selectivity for aromatics of about45%. The selectivity for benzene and toluene are about 20 and 25%,respectively.

It is intended to cover by the following claims, all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrocyclization art.

I claim as my invention:
 1. A method for dehydrocyclizing adehydrocyclizable hydrocarbon comprising contacting the hyrocarbon atdehydrocyclization conditions with a catalytic composite comprising aporous carrier material containing, on an elemental basis, about 0.01 toabout 2 wt. % platinum group metal, about 0.1 to about 5 wt. % cobalt,about 0.01 to about 2 wt. % rhenium and abot 0.1 to about 3.5 halogen;wherein the platinum group metal, catalytically available cobalt andrhenium are uniformly dispersed throughout the porous carrier material;wherein substantially all of the platinum group metal is present in theelemental metallic state; and wherein substantially all of the rheniumand catalytically available cobalt are present in the elemental metallicstate or in a state which is reducible to the element metallic stateunder dehydrocyclization conditions or in a mixture of these states. 2.A method as defined in claim 1 wherein the dehydrocyclizable hydrocarbonis admixed with hydrogen when it contacts the catalytic composite.
 3. Amethod as defined in claim 1 wherein the platinum group metal isplatinum.
 4. A method as defined in claim 1 wherein the platinum groupmetal is palladium.
 5. A method as defined in claim 1 wherein theplatinum group metal is iridium.
 6. A method as defined in claim 1wherein the platinum group metal is rhodium.
 7. A method as defined inclaim 1 wherein the porous carrier material is a refractory inorganicoxide.
 8. A method as defined in claim 7 wherein the refractoryinorganic oxide is alumina.
 9. A method as defined in claim 1 whereinthe halogen is combined chloride.
 10. A method as defined in claim 1wherein the dehydrocyclizable hydrocarbon is an aliphatic hydrocarboncontaining 6 to 20 carbon atoms per molecule.
 11. A method as defined inclaim 10 wherein the aliphatic hydrocarbon is an olefin.
 12. A method asdefined in claim 10 wherein the aliphatic hydrocarbon is a paraffin. 13.A method as defined in claim 12 wherein the paraffin hydrocarbon is aparaffin containing 6 to 10 carbon atoms per molecule.
 14. A method asdefined in claim 12 wherein the paraffin is hexane.
 15. A method asdefined in claim 12 wherein the paraffin is heptane.
 16. A method asdefined in claim 12 wherein the paraffin is octane.
 17. A method asdefined in claim 12 wherein the paraffin is nonane.
 18. A method asdefined in claim 12 wherein the paraffin is a mixture of C₆ to C₉paraffins.
 19. A method as defined in claim 2 wherein thedehydrocyclization conditions include a temperature of 800° to about1100° F., a pressure of 0 to 250 psig, a LHSV of 0.1 to 5 hr..sup.⁻¹,and a hydrogen to hydrocarbon mole ratio of about 0.1:1 to about 10:1.20. A method as defined in claim 1 wherein the composite contains, on anelemental basis, about 0.05 to about 1 wt. % platinum group metal, about0.25 to about 2.5 wt. % cobalt and about 0.05 to about 1 wt. % rheniumand about 0.05 to about 1.5 wt. % halogen.
 21. A method as defined inclaim 1 wherein the metals content of the catalytic composite isadjusted so that the automatic ratio of rhenium to platinum group metalis about 0.05:1 to about 10:1.
 22. A method as defined in claim 1wherein the metals content of the catalytic composite is adjusted sothat the atomic ratio of cobalt to platinum group metal is about 0.2:1to about 66:1.
 23. A method as defined in claim 1 wherein the contactingis performed in a substantially water-free environment.
 24. A method asdefined in claim 1 wherein the contacting is performed in asubstantially sulfur-free environment.